Research On Power System Transient Stability Analysis Method Based On Individual Machine Energy Function

Power system transient stability analysis is an important basis for safety and stability control,and is of great significance to improving the reliability of power grid operation.The large-scale interconnection of China’s power grid and the continuous increase of installed capacity of new energy have brought severe challenges to the safe and stable operation of the power system.This requires operators to identify the stable state of the system in time after the fault,determine the severity of system instability,and clear the fault accurately and quickly.Therefore,it is necessary to study the fast calculation method of power system transient stability used to help operators quickly grasp the system stability information after the fault,so as to take further measures to clear the fault.Therefore,with the aim of fast calculation of power system transient stability,using the individual machine energy function and individual equal area criterion(IMEAC),this paper proposed a power system transient stability analysis method based on the individual machine energy function.To analyze the stability characteristics of an individual machine in a multi-machines power system,this paper started from the energy conversion in the rolling ball system and verified the stability characteristics and EAC of the critical machine-system COI machine system through a series of mappings.On this basis,the rotor swing curve and power angle characteristic curve of an individual machine under different states were analyzed,and the stability of critical machines was determined by the appearance of dynamic liberation point(DLP)or dynamic stationary point(DSP)and IMEAC,the transient stability of the multi-machine power system was judged based on critical machines.Based on the stability characteristics of the critical machines and the analysis of the proportion of the transient energy of the critical machines in the global transient energy,this paper proposed a criterion for judging the stability of the system by the stability of the critical machines.After that,in order to judge the severity of system instability,the stability margin of the system was calculated according to IMEAC.On this basis,a calculation method of system fault limit clearing time based on stability margin was given.Finally,by comparing the results of time-domain simulation and transient stability calculation,the validity of calculating the fault limit clearing time based on the transient stability calculation was proved,and the problems of the global time domain simulation in obtaining the fault limit clearing time were highlighted through the comparison of case studies.In order to realize the fast identification of power system transient stability,this paper proposed a power system transient stability calculation method based on virtual linear trajectory.Firstly,a linear assumption was made for the rotor swing curves of the individual machines after the fault removal.Then,based on the virtual linear trajectory,the DLP points of the critical machines after the fault were calculated.Finally,according to the IMEAC,the stability margin and the fault limit clearing time of the system were calculated.Through the analysis of calculation examples,the feasibility and effectiveness of the individual machine method based on virtual linear trajectory in power system transient stability analysis were verified.Finally,the mechanism of inner-group motions in the cluster equivalence method was analyzed in detail,and the inner-group motion model of the individual-equivalent machine system was established.Through the analysis of calculation examples,the effectiveness of IMEAC in distinguishing the stability of the inner-group motion was verified.